This section provides background information related to the present disclosure that is not necessarily prior art. This section further provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
The detection of ice and associated icing conditions is an important factor in maximizing safety associated with various modes of transportation. It is well known that ice accumulation on surfaces can lead to an increased occurrence of vehicle accidents, personal injuries resulting from falls, and disruptions in transportation and other human activities.
In connection with vehicle travel, roadway ice can often occur in in ways that are difficult for a prudent driver to detect. Such ice—often referred to as ‘slippery ice’ or ‘black ice’—is usually smooth and translucent. Similarly, in connection with aircraft travel, airborne icing conditions can often occur in ways that are difficult for a pilot to discern. Airborne icing can occur in nearly all regions of the globe throughout the year, making detection and avoidance important for flight safety.
Unfortunately, few systems exist that are capable of reliably detecting the presence of ice or icing conditions and providing an associated alert. In terms of ground-based vehicles, such as cars, trucks, trains, automated people movers, rails, monorails, metros, buses, motorcycles, bicycles, and similar vehicles, there is a surprising lack of suitable systems for detecting and warning users of the presence of ice on surfaces, such as roadways, bridges, railways, sidewalks, or even taxiways (such as in connection with ground operations of aircraft). In fact, ice detection in most vehicles merely includes a simple notification once the air temperature is at or near the freezing point of water. However, unfortunately, this is not typically indicative of the presence of surface ice that may affect safety and/or drivability of a vehicle. This invariably leads to a high number of accidents and fatalities due to drivers and operators being unaware of deteriorating conditions or false alerts that are ultimately disregarded by a driver or operator. In terms of airborne-based vehicles, such as aircrafts, helicopters, UAVs, and similar vehicles, additional systems are available, but each suffers from a number of disadvantages.
Prior art approaches for detecting slippery ice on surfaces, such as roads, use an imager capable of measuring the polarization of the light reflected by slippery ice. However, it should be understood that although light is polarized when reflected by dielectric materials, such as ice, ice is not the only dielectric material that polarizes light. In fact, reflections by wet and/or oily surfaces also cause polarization, which would lead to false reporting of ice. Therefore, polarization is not capable of distinguishing among the possible types of dielectric materials reflecting light. Consequently, it cannot be used to detect the presence of ice unambiguously. For example, U.S. Pat. No. 2008/0129541A1 refers to a slippery ice warning system capable of monitoring the road ahead of a vehicle. One or two cameras are used to image the same scene at two orthogonal polarizations. When a single camera is used, a polarization beam splitter is used to separate the reflected light into two orthogonal polarizations. The possible (but ambiguous) determination of the existence of slippery ice ahead of the vehicle is detected by measuring the polarization of the reflected light. However, again, this system is unable to discern whether the detected polarization is due to ice or some other reflective material.
Additional ice detection systems are based on in-situ measurements and are only applied to airborne applications. For example, U.S. Pat. No. 7,104,502 is for a system capable of detecting the accumulation of ice by measuring changes in the vibration frequency of a strut exposed to the airflow on an aircraft. The strut contains at least one feature that allows ice to accrete on it at higher rate than in other parts of the aircraft. Similarly, U.S. Pat. No. 7,370,525 refers to a dual channel inflight system that detects ice accretion on aircraft surfaces. The system illuminates the surface of the aircraft with linearly polarized light. Light conductors with polarization sensitivity aligned to the transmitted light, and with polarization sensitivity orthogonal to it, acquire the backscattered light. The ratio of the intensities of the light in the two conductors is used to detect the presence of ice.
Moreover, U.S. Pat. No. 6,269,320 describes an in-situ Supercooled Large Droplet (SLD) detector. This system takes advantage of boundary layer flow patterns to detect SLD. It is capable of distinguishing between the presence of water droplets that cause regular cloud icing and SLD icing. However, this system detects ice after it accumulates on aircrafts surfaces and thus does not give warnings before a hazards situation occurs. In particular, it does not detect supercooled liquid water droplets in the airspace around aircrafts.
In some cases, prior art approaches for distinguishing between liquid water and ice particles in the airspace ahead of aircrafts measure the depolarization of the backscattered light emitted by a polarized laser beam. U.S. Pat. No. 6,819,265 refers to an ice warning system capable of monitoring the airspace ahead of the aircraft. The system contains a laser source, optical elements to direct the laser beam into the airspace ahead of the aircraft and to receive the laser light backscattered by the targets, optical elements to separate the received laser light into various wavelengths and to direct them into light detectors, and a processor to conduct the calculations necessary to generate warnings. U.S. Pat. No. 7,986,408 refers to an airborne active system that employs both linear and circular polarizations to detect water droplets and ice particles in the airspace ahead of an aircraft.
According to the principles of the present teachings, an ice and supercooled water detection system is provided that overcomes the disadvantages of the prior art and is particularly useful in ground-based and airborne-based applications. In most embodiments of the present teachings, the system detects ice unambiguously by making multi-spectral measurements of radiance. In some embodiments, the system can be passive but a light source can be included, detectors and/or a shortwave infrared (SWIR) camera with two filters, a data processor unit, and interfaces with displays, safety systems, and/or flight systems provide an indication of icing and a response to it.
Still further, in some conventional airborne applications, the detection of icing conditions in the airspace ahead of an aircraft requires systems capable of actually distinguishing between supercooled liquid water droplets and ice particles. Accordingly, in some embodiments of the present teachings, the system is capable of detecting liquid water droplets and ice particles in an area of interest of the airspace, and of estimating the size of potentially hazardous supercooled liquid water droplets. This embodiment increases aviation safety by adding the capability of detecting icing conditions and Supercooled Large Droplets (SLD) to flight displays such as Enhanced Vision Systems (EVS).
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.